JP2019074381A - Decontamination device and decontamination method of radioactive metallic waste - Google Patents

Abstract

To provide a decontamination device and a decontamination method, capable of easily cleaning the metallic wastes stuck to an electrode serving as a negative electrode during decontamination.SOLUTION: A decontamination device comprises a storage tank, a power supply device, a first electrode, and a connection member selectively connected to a radioactive metallic waste and a second electrode. The connection member can be switched to a first position and a second position. In the first position, the radioactive metallic waste or the second electrode is arranged in the storage tank with the first electrode arranged in the storage tank. In the second position, the radioactive metallic waste or the second electrode is arranged outside the storage tank. The decontamination device is in the first position with the connection member connected to the radioactive metallic waste. When the connection member is connected to the radioactive metallic waste and in the first position and the power supply device applies voltage so that the first electrode serves as the negative electrode, the decontamination device decontaminates the radioactive metallic waste. When the connection member is set to the second position, the member connected to the connection member outside the storage tank is allowed to switch between the radioactive metallic waste and the second electrode. When the connection member is connected to the second electrode and in the first position and the power supply device applies voltage so that the first electrode serves as a positive electrode, the decontamination device cleans the metal deposit adhering to the first electrode.SELECTED DRAWING: Figure 6

Description

  The technology disclosed herein relates to a decontamination apparatus and a decontamination method for decontaminating radioactive metal waste by electropolishing.

  Among nuclear power plants and facilities handling radioactive materials, among metal wastes generated with the abolition, dismantling, or operation of facilities, metal wastes whose radioactivity level is above the standard value (hereinafter also referred to as radioactive metal wastes) Is included. From the viewpoint of disposal, it is desirable that these metal wastes be treated after the surface is decontaminated to reduce the activity level to below the standard value. As a method of decontamination of radioactive metal waste, a technology for removing the surface of the radioactive metal waste by electropolishing etc. has been developed. For example, in the decontamination apparatus of patent document 1, the anode stand connected to the anode jig | tool is installed in the storage tank, and the cylindrical radioactive metal waste is installed in the upper part of the anode stand. The cylindrical radioactive metal waste is placed on the anode base so that the axial direction is horizontal. Further, a cathode jig is installed in the storage tank, and a cathode is connected to the cathode jig. The cathode is installed axially through the interior of the cylindrical radioactive metal waste. When a voltage is applied between the anode jig and the cathode jig, the surface of the radioactive metal waste is electropolished.

JP 3-17600 A

  In the decontamination apparatus as described in Patent Document 1, when a voltage is applied between the anode and the cathode, metal dissolves from the radioactive metal waste into the electrolyte. As the dissolved metal gradually adheres to the surface of the cathode, the decontamination ability of the decontamination apparatus decreases with the passage of time. For this reason, when the decontamination ability falls below a preset level, it is necessary to clean the metal deposit attached to the cathode. As a method of cleaning the cathode, for example, there is known a method in which a voltage in the reverse direction to that at the time of decontamination is applied to the cathode, and metal deposits adhered to the cathode are redissolved in the electrolyte. However, in the decontamination apparatus of Patent Document 1, in order to apply a voltage in the reverse direction to the cathode, the radioactive metal waste and the cathode installed in the storage tank at the time of decontamination are taken out of the storage tank and attached with metal. It is necessary to reconnect to the power supply device the negative electrode to which the adherend adheres and the electrode that becomes the negative electrode when applying a voltage in the reverse direction, and to re-install these electrodes in the storage tank, which increases the work load There was a problem that. The present specification discloses a technique for easily cleaning metal deposits attached to an electrode which becomes a cathode during decontamination.

  The decontamination apparatus disclosed herein decontaminates radioactive metal waste by electropolishing. The decontamination apparatus can be disposed in the storage tank in which the electrolytic solution is stored, the power supply apparatus, and the storage tank, and can be electrically connected to the first electrode electrically connected to the power supply apparatus and the power supply apparatus. And a connection member selectively connected to the radioactive metal waste and the second electrode. The connecting member is a first position where the radioactive metal waste or the second electrode is disposed in the reservoir while the first electrode is disposed in the reservoir, the radioactive metal waste outside the reservoir Alternatively, it can be switched to the second position where the second electrode is disposed. The decontamination apparatus is at a first position with the connection member connected to the radioactive metal waste, and the power supply device is configured such that the first electrode becomes a cathode and the radioactive metal waste becomes an anode. By applying a voltage, radioactive metal waste is decontaminated by electropolishing. In the decontamination apparatus, by setting the connection member to the second position in a state where the first electrode is disposed in the storage tank, the member connected to the connection member outside the storage tank is a radioactive metal waste and Switch between the second electrode. Furthermore, the decontamination apparatus is at the first position with the connection member connected to the second electrode, and the power supply device has the second electrode as a cathode and the first electrode as an anode. By applying a voltage as described above, the metal deposit attached to the first electrode is cleaned.

  In the above decontamination apparatus, the radioactive metal waste or the second electrode can be selectively connected to the connecting member outside the storage tank by switching the connecting member to the first position and the second position. For this reason, the second electrode can be installed in the storage tank instead of the radioactive metal waste without taking out the first electrode to be the cathode part from the storage tank at the time of decontamination. Therefore, the work load for cleaning the first electrode can be reduced, and the first electrode can be easily cleaned.

  In addition, the decontamination method disclosed herein decontaminates radioactive metal waste by electropolishing. The decontamination method includes a first immersion step of immersing radioactive metal waste electrically connected to the power supply device in the electrolyte, radioactive metal waste immersed in the electrolyte by the first immersion step, and the electrolyte A first voltage application step of applying a forward voltage to a first electrode disposed in the first electrode and electrically connected to the power supply device, and in a state in which the first electrode is disposed in the electrolyte, A step of removing radioactive metal waste from the electrolyte, a second immersing step of immersing the second electrode electrically connected to the power source device into the electrolyte after the removing step, a first electrode, and a second And V. a second voltage application step of applying a voltage in a reverse direction to the second electrode immersed in the electrolytic solution by the immersion step.

  In the above decontamination method, the radioactive metal waste can be decontaminated by the first voltage application step, and the metal deposit attached to the first electrode can be cleaned by the second voltage application step. In addition, the radioactive metal waste and the second electrode can be interchanged by the removal step and the second immersion step without removing the first electrode from the electrolytic solution. For this reason, the operation | work burden for washing | cleaning a 1st electrode can be eased, and a 1st electrode can be wash | cleaned easily.

BRIEF DESCRIPTION OF THE DRAWINGS The figure which shows typically schematic structure of the decontamination apparatus which concerns on an Example. The perspective view which shows the structure of a fixing jig. The perspective view which shows the structure of a holding jig. It is a top view which shows the structure of a holding part, and shows the state which the holding part holds the radioactive metal waste. It is a top view which shows the structure of a holding part, and shows the state which the holding part is holding the metal plate. The flowchart which shows an example of the method of decontaminating radioactive metal waste using the decontamination apparatus which concerns on an Example. It is a figure which shows the relationship of the voltage value and time between an electrode part and a metal plate at the time of washing | cleaning of an electrode part, (a) is a voltage value and time between an electrode part and a metal plate with which the decontamination apparatus of a present Example is equipped. (B) shows the relationship between the voltage value between the stainless steel electrode (comparative example) and the metal plate and the time.

  The main features of the embodiment described below are listed. The technical elements described below are technical elements that are independent of each other and exhibit technical usefulness by themselves or various combinations, and are not limited to the combinations described in the claims at the time of filing. Absent.

(Feature 1) In the decontamination apparatus disclosed in the present specification, the first electrode may be formed of a metal belonging to a titanium group. According to such a configuration, when the metal deposit attached to the first electrode is cleaned, it is possible to prevent the first electrode itself from being dissolved. Therefore, the durability of the first electrode can be improved. In addition, when the first electrode is formed of a metal belonging to the titanium group, the first electrode itself is difficult to dissolve when cleaning the metal deposit attached to the first electrode, and the first electrode is attached to the first electrode. Metal deposit dissolves. Thus, the state of dissolution of metal deposits on the first electrode can be detected by monitoring the electrical behavior between the first electrode and the second electrode. For this reason, it can be avoided that the work of cleaning the first electrode becomes unnecessarily long.

(Feature 2) In the decontamination apparatus disclosed herein, the radioactive metal waste may be cylindrical. The connection member may include a grip for holding the radioactive metal waste such that the axial direction of the radioactive metal waste is vertical when the connection member is positioned at the first position. According to such a configuration, when the radioactive metal waste is cylindrical, the cylindrical radioactive metal waste can be stably held in the reservoir by holding the radioactive metal waste by the connection member. Can.

(Feature 3) In the decontamination method disclosed in the present specification, the first electrode may be formed of a metal belonging to a titanium group. In the second voltage application step, the first voltage is applied based on at least one of a voltage applied between the first electrode and the second electrode and a current flowing between the first electrode and the second electrode. The application of the reverse voltage between the second electrode and the second electrode may be stopped. According to such a configuration, by forming the first electrode from a metal belonging to the titanium group, it is possible to detect the state of dissolution of the deposit attached to the first electrode. Therefore, in the second voltage application process, it can be detected that the cleaning of the first electrode is completed, and it can be avoided that the cleaning operation of the first electrode becomes unnecessarily long.

  Hereinafter, the decontamination apparatus 10 which concerns on an Example is demonstrated. The decontamination apparatus 10 decontaminates cylindrical radioactive metal waste 2 such as piping installed in, for example, a nuclear power plant or a facility handling radioactive materials. In the case of piping and the like, since the component including the radioactive substance passes through the inner circumference of the piping and the like, the inner surface thereof is contaminated with the radioactive substance. For this reason, the decontamination apparatus 10 of this embodiment is configured to electropolish the inner surface of the cylindrical radioactive metal waste 2. As shown in FIG. 1, the decontamination apparatus 10 includes a storage tank 12, a power supply device 16, a fixing jig 20 for fixing an electrode portion 22 described later, and a holding jig 40 capable of holding the radioactive metal waste 2. Is equipped.

  The storage tank 12 has a box-like shape whose upper surface is released. The surface of the storage tank 12 is covered with an insulating material, and is insulated from the fixing jig 20 and the holding jig 40. The fixing jig 20 and the holding jig 40 can be inserted into the storage tank 12 from above. The storage tank 12 is filled with the electrolyte solution 14. A filtering device (not shown) is connected to the storage tank 12. The electrolyte solution 14 stored in the storage tank 12 is sent out to the filtration device, filtered, and returned to the storage tank 12. That is, the electrolyte solution 14 is circulated between the storage tank 12 and the filtration device. The electrolytic solution 14 may be a known electrolytic solution used for electrolytic polishing, and for example, an electrolytic solution containing a phosphoric acid solution may be used. With the radioactive metal waste 2 and the electrode part 22 immersed in the electrolyte solution 14, the radioactive metal waste 2 is connected to the anode of the power supply device 16 and the electrode part 22 is connected to the cathode of the power supply device 16 to When flowing, the surface of the radioactive metal waste 2 dissolves electrochemically. That is, the metal such as iron constituting the surface of the radioactive metal waste 2 and the radioactive substance attached to the surface are dissolved in the electrolyte solution 14.

  The fixing jig 20 will be described with reference to FIG. When the radioactive metal waste 2 is to be decontaminated, the fixing jig 20 has an electrode portion 22 which is to be a cathode fixed. By disposing the fixing jig 20 in the storage tank 12, the electrode unit 22 is disposed in the storage tank 12. As shown in FIG. 2, the fixing jig 20 includes a plurality of electrode portions 22, a lower plate 24, a frame 28, a connection portion 36, and a guide portion 38. The surfaces of the lower plate 24, the frame 28 and the guide portion 38 are covered with an insulating material so that the surfaces are not electropolished. The guide portion 38 may be formed of a non-conductive material so that the surface thereof is not electropolished.

  The electrode portion 22 is rod-shaped and made of titanium. When the electrode portion 22 is formed of titanium, it is possible to prevent the electrode portion 22 itself from being dissolved in the electrolyte solution 14 together with the attached metal when the metal attached to the electrode portion 22 is cleaned. In addition, although the electrode part 22 of a present Example is formed with titanium, it is not limited to such a structure. For example, the electrode portion 22 may be formed of a metal belonging to a titanium group such as zirconium. The electrode portion 22 is disposed on the lower plate 24 perpendicularly to the lower plate 24 (in the Z direction in FIG. 2). A plurality of electrode portions 22 are disposed on the lower plate 24, and the dimensions in the height direction (that is, the Z direction) of the plurality of electrode portions 22 substantially coincide with each other. In the present embodiment, ten electrode portions 22 are arranged in five rows and two rows. Specifically, five electrode portions 22 are disposed on a straight line extending in the X direction, and the remaining five electrode portions 22 are disposed at positions substantially equidistantly spaced from each of the five electrode portions 22 in the Y direction. It is done. In the present embodiment, the fixing jig 20 is provided with ten electrode parts 22, but the number of the electrode parts 22 is not particularly limited, and may be more than ten, or more than ten. It may be less. The electrode unit 22 is an example of a “first electrode”.

  The lower plate 24 has a substantially rectangular flat plate shape in plan view, and is formed of stainless steel. The dimension of the lower plate 24 in the X direction is larger than the dimension in the Y direction. Ten electrode portions 22 are vertically fixed to the upper surface of the lower plate 24 upward. As described above, the lower plate 24 is formed of stainless steel, and the electrode portion 22 is formed of titanium. Therefore, the charge flowing to the lower plate 24 flows from the lower plate 24 to the electrode portion 22. The lower plate 24 is also provided with a plurality of through holes 26. The through holes 26 are arc-shaped, and two through holes 26 are disposed at positions surrounding one electrode portion 22. As described later, when the radioactive metal waste 2 is disposed in the storage tank 12, the electrode portion 22 is located in the inner circumference of the radioactive metal waste 2. The through hole 26 is formed to be located between the electrode portion 22 and the inner periphery of the radioactive metal waste 2 when the radioactive metal waste 2 is disposed in the storage tank 12 in a plan view. By providing the through holes 26 in the lower plate 24, the electrolytic solution 14 can pass through the through holes 26 and can be suitably circulated between the radioactive metal waste 2 and the electrode portion 22.

  The frame 28 is formed of stainless steel and comprises four sides 30 and a top 32. The side portion 30 is a plate shape elongated in the Z direction, the lower end is connected to the lower plate 24, and the upper end is connected to the upper portion 32. Specifically, the lower ends of the side portions 30 are bent substantially at right angles so as to be parallel to the lower plate 24, and the bent portions are joined to the lower plate 24. The upper end of the side portion 30 projects outward (in the Y direction in FIG. 2) outside the lower plate 24 in a plan view, and is bent substantially at a right angle so as to be parallel to the upper portion 32. The dimension in the X direction of the outer periphery of the side portion 30 and the lower plate 24 is smaller than the dimension in the X direction of the inner periphery of the storage tank 12 in plan view, and Y in the outer periphery of the side portion 30 and the lower plate 24 The dimension of the direction is smaller than the dimension of the inner circumference of the storage tank 12 in the Y direction. Therefore, when the fixing jig 20 is installed in the reservoir 12, the side portion 30 and the lower plate 24 are disposed in the reservoir 12.

  The upper portion 32 is disposed at the upper portion of the fixing jig 20 and joined to the four side portions 30. The upper portion 32 is disposed parallel to the lower plate 24. The upper portion 32 has a substantially rectangular outer periphery and a substantially rectangular inner periphery having a certain width from the outer periphery. The inner periphery of the upper portion 32 is sized to substantially coincide with the outer periphery of the lower plate 24 in plan view. Therefore, the upper portion 32 protrudes to the + Y direction side and the −Y direction side from the lower plate 24 when viewed along the X direction. Further, the upper portion 32 protrudes to the + X direction side and the −X direction side from the lower plate 24 and the side portion 30 when viewed along the Y direction. The upper portion 32 is provided with a recess 34 near the center of a portion extending along the Y direction. The recess 34 is shaped to engage with a support portion 72 of a holding jig 40 described later. In addition, since the surface of the recess 34 is covered with the insulating material, the upper portion 32 (i.e., the fixing jig 20) and the support portion 72 (i.e., the holding jig 40) are not electrically connected. .

  Four connection portions 36 are connected to the upper portion 32, and two connection portions 36 are disposed at positions projecting in the + X direction side from the upper portion 32 in plan view, and 2 in a position projecting in the −X direction side from the upper portion 32. One is arranged. In other words, the connection portions 36 are disposed on both sides of the two concave portions 34 and project outside the upper portion 32. When the fixing jig 20 is installed in the storage tank 12, the four connection parts 36 abut the upper surface of the storage tank 12. Further, the connection unit 36 is electrically connected to the power supply device 16. The charge flowing from the power supply 16 flows from the lower plate 24 to the electrode portion 22 in the order of the connection portion 36, the upper portion 32, the side portion 30 and the lower plate 24. Therefore, when the cathode of the power supply device 16 and the connection portion 36 are connected, the electrode portion 22 functions as a cathode, and when the anode of the power supply device 16 and the connection portion 36 are connected, the electrode portion 22 functions as an anode. In the present embodiment, when the fixing jig 20 is installed in the storage tank 12, the four connection parts 36 abut the upper surface of the storage tank 12, but the upper portion 32 (specifically, in the Y direction of the upper portion 32) The portion extending along may be in contact with the upper surface of the reservoir 12.

  Two guide portions 38 are provided vertically on the lower plate 24 (that is, in the Z direction) on the lower plate 24. The two guide portions 38 are disposed in the vicinity of the corner of the diagonal position of the lower plate 24. Specifically, the vicinity of the corner of the lower plate 24 in the + X direction and the -Y direction, -X direction and It is arranged at two places near the corner in the + Y direction. The guide portion 38 is used to position the holding jig 40. In the present embodiment, the guide portion 38 is disposed in the vicinity of the two corner portions of the lower plate 24. However, the present invention is not limited to such a configuration. The positioning position of the guide portion 38 is not limited as long as the holding jig 40 can be positioned by the guide portion 38, and the shape of the guide portion 38 is not limited. Further, the number of the guide portions 38 is not limited, and may be one or three or more.

  The holding jig 40 will be described with reference to FIGS. 3 to 5. The holding jig 40 selectively holds the radioactive metal waste 2 or the metal plate 4 and can be installed in the fixing jig 20. The holding jig 40 is an example of the “connection member”. As shown in FIG. 3, the holding jig 40 includes a placement unit 42, a grip unit 50, a frame 70, a support unit 72, and a removal unit 76. The surfaces of the mounting portion 42, the frame 70, and the extraction portion 76 are covered with an insulating material. The lead-out portion 76 may be formed of a nonconductive material.

  The mounting unit 42 is disposed below the holding jig 40 and mounts the radioactive metal waste 2 or the metal plate 4. The placement unit 42 includes a bottom 44, a side 46, and a guide 48.

  The bottom portion 44 has a substantially rectangular outer periphery in a plan view, and the size of the outer periphery is smaller than the size of the inner periphery of the upper portion 32. The bottom portion 44 has members arranged in a lattice, and when the holding jig 40 is arranged in the fixing jig 20, the electrode portion 22 passes between the lattices. The bottom portion 44 has a grid shape, so that the electrolyte solution 14 can pass between the grids provided on the bottom portion 44. Therefore, when the holding jig 40 is taken out of the storage tank 12, the amount of the electrolytic solution 14 carried out of the storage tank 12 together with the holding jig 40 can be reduced. The size of the grid provided in the bottom 44 is not particularly limited, but when the radioactive metal waste 2 or the metal plate 4 is disposed on the bottom 44, the size that the radioactive metal waste 2 and the metal plate 4 do not pass It is preferable that Further, in the present embodiment, the bottom portion 44 has a lattice shape, but the electrode portion 22 and the electrolyte solution 14 can pass through, and the radioactive metal waste 2 or the metal plate 4 can be placed thereon. For example, the bottom portion 44 may be a plate material (for example, a punching metal) provided with a plurality of through holes, or a net-like member.

  The side portion 46 is plate-like, and is connected to the bottom portion 44 and a connecting portion 68 described later. The side portions 46 are connected to both ends of the bottom portion 44 in the X direction, and are disposed perpendicularly to the bottom portion 44. The lower portion of the side portion 46 is joined to the bottom portion 44, and its plate width gradually decreases from the bottom to the top. A connecting portion 68 is joined to the upper end side of the side portion 46.

  The guide portion 48 protrudes to the outside of the bottom portion 44, and in the present embodiment, protrudes to the + X direction side and the −X direction side (not shown) of the bottom portion 44. The guide portion 48 is provided with a guide hole 48 a. The guide hole 48 a has a dimension such that the rod-shaped guide portion 38 can pass therethrough, and is disposed at a position corresponding to the guide portion 38. That is, when the holding jig 40 is installed in the fixing jig 20, the guide hole 48a is disposed at a position where the guide portion 38 penetrates. The holding jig 40 can be installed at an appropriate position in the fixing jig 20 by the fixing jig 20 including the guide portion 38 and the holding jig 40 including the guide hole 48 a.

  The gripping portion 50 selectively grips the radioactive metal waste 2 or the metal plate 4. The grip 50 is disposed between the two sides 46. The gripping portion 50 includes a first member 52, a second member 62, and a connecting portion 68 fixed to the side portion 46. The radioactive metal waste 2 or the metal plate 4 is disposed between the first member 52 and the second member 62. In addition, the surfaces other than the site | part which contacts the radioactive metal waste 2 or the metal plate 4 of the holding part 50 are covered with an insulating material, and these surfaces are not electropolished.

  The first member 52 has a substantially rectangular parallelepiped shape and is formed of stainless steel. The first member 52 extends in the X direction, and a plurality of grooves 54 are provided on both side surfaces extending along the X direction. The grooves 54 extend in the Z direction, and are provided at three locations on the side surface on the -Y direction side of the first member 52 in this embodiment, and at three locations on the side surface on the + Y direction side of the first member 52 ing. As shown in FIG. 4, the grooves 54 are side surfaces 56a and 56b perpendicular to the side surface 52a extending along the X direction of the first member 52 (that is, parallel to the YZ plane), and side surfaces 56a parallel to the side surface 52a, It has a side surface 58 perpendicular to 56b (ie, parallel to the XZ plane).

  The groove 54 is located at a position where the electrode portion 22 coincides with the central portion (central portion in the X direction) of the side surface 58 when viewed along the Y direction with the holding jig 40 installed in the fixing jig 20. Provided. In the present embodiment, the grooves 54 are provided at positions corresponding to the six electrode portions 22 disposed at the center among the ten electrode portions 22 when viewed along the Y direction, and The groove 54 is not provided at a position corresponding to the electrode portion 22 of the book. In addition, the position and number which provide the groove | channel 54 are not specifically limited, According to the position and number of the radioactive metal waste 2 hold | maintained at the holding jig 40, it can set suitably. That is, the grooves 54 may be provided at positions corresponding to the electrode portions 22 in which the radioactive metal waste 2 is disposed, and the number of grooves 54 is not limited. The dimensions of the side surfaces 56 a, 56 b, 58 are determined to the size of the radioactive metal waste 2. Specifically, the dimensions of the side surfaces 56 a, 56 b, 58 are such that when the radioactive metal waste 2 is placed in contact with the first member 52, the radioactive metal waste 2 and the first member 52 have two edges of the groove 54. It is dimensioned to contact only the portions 60a, 60b (i.e., the edge bounding the side surfaces 52a and 56a, 56b). By dimensioning the groove 54 in this manner, the radioactive metal waste 2 can be engaged with the groove 54 and the radioactive metal waste 2 can be stably held. In addition, since the radioactive metal waste 2 does not contact the side surface 58 of the groove 54, the contact portion between the radioactive metal waste 2 and the first member 52 can be reduced.

  That is, when the dimension of the side surfaces 56a and 56b in the Y direction is too small, the depth (dimension in the Y direction) of the groove 54 becomes shallow, and the radioactive metal waste 2 contacts the side surface 58. Then, the contact points of the radioactive metal waste 2 and the first member 52 increase. Also, if the dimension of the side surface 58 is too small, the radioactive metal waste 2 will not be able to engage with the groove 54, and the radioactive metal waste 2 can not be held stably. If the dimension of the side surface 58 is too large, the radioactive metal waste 2 will be accommodated in the groove 54 and will not be in contact with both edges 60 a, 60 b of the groove 54. Therefore, the radioactive metal waste 2 does not engage with the groove 54, and the radioactive metal waste 2 can not be stably held. By providing the groove 54 having the above-described configuration in the first member 52, the radioactive metal waste 2 can be stably held. Furthermore, when the holding jig 40 is removed from the storage tank 12, the electrolytic solution 14 is between the radioactive metal waste 2 and the first member 52 by reducing the contact portion between the radioactive metal waste 2 and the first member 52. It becomes difficult to retain, and the amount of the electrolyte solution 14 carried out of the storage tank 12 can be reduced. In particular, in the present embodiment, since the radioactive metal waste 2 contacts only the two edge portions 60a and 60b of the groove 54, the clearance between the radioactive metal waste 2 and the first member 52 in the vicinity of the contact portion is wide. be able to. As a result, the surface tension of the electrolyte solution 14 can reduce the amount of the electrolyte solution 14 held between the radioactive metal waste 2 and the first member 52. Thereby, the quantity of the electrolyte solution 14 carried out out of the storage tank 12 can be reduced suitably.

  The first member 52 is detachably mounted to the connecting portion 68 fixed to the side portion 46. Holding the radioactive metal waste having a diameter different from that of the radioactive metal waste 2 or the metal plate 4 of various dimensions in the holding jig 40 by changing the type of the first member attached to the connecting portion 68 Can.

  The second member 62 has a substantially rectangular flat plate shape, and is disposed parallel to the first member 52 in the X direction and spaced apart in the Y direction. One second member 62 is disposed on each of the + Y direction side and the −Y direction side of the first member 52. Each second member 62 is connected to the first member 52 by a bolt 64. Two bolts 64 are disposed for each second member 62, and one each is provided in the vicinity of both ends of the first member 52 (that is, the end in the + X direction and the end in the −X direction). It is arranged one by one. By adjusting the screwing amount of the bolt 64 into the first member 52, the distance between the first member 52 and the second member 62 can be adjusted.

  Between the second member 62 and the first member 52, either the radioactive metal waste 2 or the metal plate 4 is disposed. By tightening the bolt 64, the radioactive metal waste 2 or the metal plate 4 is held between the first member 52 and the second member 62. When the radioactive metal waste 2 is disposed between the second member 62 and the first member 52, one to six radioactive metal wastes 2 should be held according to the position where the groove 54 is provided. Can.

  When arranging the metal plate 4 between the second member 62 and the first member 52 as shown in FIG. 4 and FIG. 5, one each in the + Y direction side and the −Y direction side of the first member 52 A metal plate 4 is disposed. The metal plate 4 has a substantially rectangular plate shape and is formed of stainless steel. The dimension of the metal plate 4 in the X direction is shorter than the distance between the two bolts 64 connecting each second member 62 to the first member 52. For this reason, the metal plate 4 can be disposed between the second member 62 and the first member 52 in a state of being placed on the bottom portion 44. Further, as shown in FIG. 5, when the holding jig 40 is installed in the fixing jig 20, the thickness (dimension in the Y direction) of the metal plate 4 is between the first member 52 and the electrode portion 22. The dimensions are such that the metal plate 4 and the second member 62 can be accommodated. Therefore, the dimension of the metal plate 4 in the Y direction is smaller than the dimension of the radioactive metal waste 2 in the Y direction. By making the distance between the first member 52 and the second member 62 smaller than that in the case where the radioactive metal waste 2 is disposed, the first member 52 and the second member 62 can be obtained. And the first member 52 (specifically, the side surface 52a) can be electrically connected. The metal plate 4 is an example of the “second electrode”.

  Further, a shock absorbing material 66 is disposed on the surface of the second member 62 facing the first member 52. Even if there is an error in the diameter of the radioactive metal waste 2 (three in the present embodiment) disposed between the second member 62 and the first member 52 due to the shock absorbing material 66, the plurality of radioactive metal wastes 2 All can be stably held.

  The frame 70 is formed of stainless steel and extends in the Z direction in a long manner. The frame 70 is connected to the connecting portion 68, and the two frames 70 are connected to the connecting portion 68 disposed on the −X direction side and the connecting portion 68 disposed on the + X direction side.

  The support portion 72 is in the form of a plate elongated in the X direction, and is made of stainless steel. The dimension of the support portion 72 in the X direction is the dimension of the fixing jig 20 in the X direction (that is, from the connecting portion 36 installed in the −X direction to the connecting portion 36 installed in the + X direction in the fixing jig 20). Length). The dimension of the support portion 72 in the Y direction is smaller than the dimension of the entire holding jig 40 in the Y direction, and is dimensioned to engage with the recess 34. The support portion 72 is disposed at an upper portion of the holding jig 40 and a substantially central position in the Y direction of the holding jig 40. The support portion 72 is connected to the frame 70 and protrudes in the + X direction side and the −X direction side of the frame 70. As described above, the support portion 72 and the recess 34 of the fixing jig 20 are insulated.

  Connection portions 74 electrically connected to the power supply device 16 are disposed at both ends of the support portion 72. The charge flowing from the power supply device 16 flows in the order of the support portion 72, the frame 70, the connection portion 68, and the first member 52. Then, when the radioactive metal waste 2 is disposed in the grip portion 50, the charge flowing to the first member 52 flows to the radioactive metal waste 2. Further, in the case where the metal plate 4 is disposed in the grip portion 50, the charge that has flowed to the first member 52 flows to the metal plate 4.

  When the radioactive metal waste 2 is disposed in the grip portion 50, the anode of the power supply device 16 and the connection portion 74 are connected. Then, the radioactive metal waste 2 functions as an anode. When the holding jig 40 is installed in the storage tank 12 in a state where the radioactive metal waste 2 is disposed in the holding unit 50, the electrode portion 22 is inserted into the inner circumference of the radioactive metal waste 2. In this state, when the fixing jig 20 is connected to the cathode of the power supply device 16 and the holding jig 40 is connected to the anode of the power supply device 16, current flows between the electrode portion 22 and the inner surface of the radioactive metal waste 2. The metal dissolves in the electrolyte 14 from the inner surface of the radioactive metal waste 2 in the flow. That is, the radioactive substance adhering to the surface dissolves in the electrolyte solution 14 together with the metal constituting the inner surface of the radioactive metal waste 2. Thereby, the inner surface of the radioactive metal waste 2 can be decontaminated. When the decontamination treatment is continued, the metal dissolved in the electrolyte solution 14 gradually adheres to the surface of the electrode portion 22.

  On the other hand, when the metal plate 4 is disposed in the grip portion 50, the cathode of the power supply device 16 and the connection portion 74 are connected. Then, the metal plate 4 functions as a cathode. When the holding jig 40 is installed in the storage tank 12 in a state in which the metal plate 4 is disposed in the grip portion 50, the metal plate 4 and the electrode portion 22 face each other. In this state, when the fixing jig 20 is connected to the anode of the power supply device 16 and the holding jig 40 is connected to the cathode of the power supply device 16, a current flows between the electrode portion 22 and the metal plate 4. Then, the metal attached to the surface of the electrode portion 22 is dissolved in the electrolytic solution 14. By such decontamination treatment, the metal attached to the surface of the electrode portion 22 can be cleaned.

  In the present embodiment, the metal plate 4 is held by the holding portion 50 using the first member 52 and the second member 62 used when holding the radioactive metal waste 2, but such a configuration It is not limited. The metal plate 4 is electrically connected to the power supply device 16 and is held by the holding jig 40. When the holding jig 40 is installed in the fixing jig 20, the metal plate 4 faces the electrode portion 22. It may be arranged at a position. For example, the first and second members dedicated to holding the metal plate 4 may be installed in the holding jig 40 to hold the metal plate 4 on the holding jig 40. However, when the radioactive metal waste 2 or the metal plate 4 is selectively held using the same first member 52 and second member 62, it is not necessary to manufacture a plurality of types of first members 52 and second members 62. . For this reason, while being able to hold down a manufacturing cost, the space for storing several types of 1st members and 2nd members can be reduced. Moreover, the shape of the metal member which becomes a cathode at the time of washing | cleaning of the electrode part 22 is not limited to the plate shape extended along an X direction. For example, the metal member which becomes a cathode at the time of cleaning of the electrode portion 22 may be a plate material extending in the Y direction. For example, when the holding jig 40 is disposed in the fixing jig 20, the plurality of metal plates are held by the holding portion 50 so as to be located between the adjacent electrode portions 22 and separate the adjacent electrode portions 22. May be Moreover, the metal member which becomes a cathode at the time of washing | cleaning of the electrode part 22 may be cylindrical shape.

  The takeout portion 76 is a plate extending in the Y direction, and is connected to the upper surface of the support portion 72. A projection 78 is attached to the top of the take-out portion 76. The entire holding jig 40 can be taken out of the storage tank 12 by holding the projection 78 and lifting it upward by a crane not shown. Therefore, only the holding jig 40 can be taken out of the storage tank 12 while the fixing jig 20 is disposed in the storage tank 12. Further, the takeout portion 76 is installed above the guide hole 48a, and the takeout portion 76 is provided with a guide hole 80 at a position coincident with the guide hole 48a in plan view. Therefore, when the holding jig 40 is accommodated in the fixing jig 20, the guide portion 38 penetrates the guide hole 48 a and further penetrates the guide hole 80. By providing the guide holes 80, the holding jig 40 can be disposed at an appropriate position. In the present embodiment, the guide hole 80 is provided in the takeout portion 76, but the present invention is not limited to such a configuration. The guide hole 80 may be provided at a position corresponding to the guide hole 48 a in plan view, and may be provided at a member other than the takeout portion 76.

  In the decontamination apparatus 10 of the present embodiment, the radioactive metal waste 2 and the metal plate 4 can be selectively installed on the holding jig 40. Further, only the holding jig 40 can be taken out without taking out the fixing jig 20. Therefore, the radioactive metal waste 2 installed on the holding jig 40 and the metal plate 4 can be interchanged without removing the electrode portion 22 functioning as a cathode from the storage tank 12 at the time of decontamination. Therefore, the workload for cleaning the electrode unit 22 can be reduced.

  Next, with reference to FIG.6 and FIG.7, the decontamination method of the radioactive metal waste 2 using the decontamination apparatus 10 of a present Example is demonstrated. In the decontamination apparatus 10, the radioactive metal waste 2 is decontaminated, and a metal (hereinafter also referred to as a metal attached substance) attached to the electrode portion 22 by the decontaminating process is cleaned.

  As shown in FIG. 6, first, the radioactive metal waste 2 is placed on the holding jig 40 (S12). Installation of the radioactive metal waste 2 on the holding jig 40 is performed in the following procedure. First, outside the storage tank 12, the first member 52 suitable for the diameter of the radioactive metal waste 2 to be subjected to the decontamination treatment is attached to the holding jig 40. Then, the radioactive metal waste 2 is placed on the placement unit 42. At this time, the side surface of the radioactive metal waste 2 is placed at a position in contact with the edge portions 60 a and 60 b of the groove 54. As described above, since six grooves 54 are provided in the first member 52, six radioactive metal wastes 2 are placed according to the positions of the grooves 54. The number of radioactive metal wastes 2 to be placed may be smaller than six. After the radioactive metal waste 2 is placed on the placement unit 42, the position of the second member 62 is adjusted so that the radioactive metal waste 2 is gripped between the first member 52 and the second member 62. Then, the radioactive metal waste 2 is placed on the holding jig 40.

  Next, the holding jig 40 on which the radioactive metal waste 2 is placed in step S12 is disposed in the storage tank 12 (S14). The electrolytic solution 14 is accommodated in the storage tank 12 and the fixing jig 20 is further disposed. The holding jig 40 is disposed in the fixing jig 20 disposed in the storage tank 12. Specifically, the holding jig 40 is inserted into the fixing jig 20 while the two guide portions 38 are respectively penetrated into the guide holes 48 a. Furthermore, two guide portions 38 are respectively penetrated into the guide holes 80, and the support portions 72 are engaged with the recess 34. Thus, the holding jig 40 is disposed in the fixing jig 20. When the holding jig 40 is disposed in the fixing jig 20, the electrode portion 22 is positioned within the inner circumference of the radioactive metal waste 2. Step S14 is an example of the "first immersion step".

  Next, the connection portion 36 of the fixing jig 20 is connected to the cathode of the power supply device 16, the connection portion 74 of the holding jig 40 is connected to the anode of the power supply device 16, and between the two connection portions 36 and 74. A voltage is applied (S16). Then, a voltage is applied between the electrode portion 22 and the inner surface of the radioactive metal waste 2, and the metal dissolves in the electrolyte 14 from the inner surface of the radioactive metal waste 2 functioning as an anode. Thereby, the inner surface of the radioactive metal waste 2 is decontaminated. At this time, the metal dissolved in the electrolyte solution 14 gradually adheres to the surface of the electrode portion 22 which functions as a cathode. Step S16 is an example of the “first voltage application process”.

  When the inner surface of the radioactive metal waste 2 is decontaminated, the holding jig 40 is removed from the storage tank 12 (S18). At this time, the holding jig 40 can be taken out with the fixing jig 20 disposed in the storage tank 12. Specifically, the projection 78 is gripped by a crane (not shown) to lift the holding jig 40 upward. Then, only the holding jig 40 is taken out of the storage tank 12. Step S18 is an example of the "extraction process".

  Next, the radioactive metal waste 2 is removed from the holding jig 40, and the metal plate 4 is placed on the holding jig 40 (S20). The installation of the metal plate 4 on the holding jig 40 is performed in the following procedure. First, the bolt 64 is adjusted to separate the second member 62 from the first member 52. Then, the radioactive metal waste 2 is removed from the holding jig 40. Thereafter, the metal plate 4 is placed on the placement unit 42. At this time, the metal plate 4 is placed at a position where one surface of the metal plate 4 contacts the side surface 52 a of the first member 52. Then, the position of the second member 62 is adjusted such that the metal plate 4 is fixed between the first member 52 and the second member 62. Then, the metal plate 4 is held by the holding jig 40.

  Next, the holding jig 40 on which the metal plate 4 is installed in step S20 is disposed in the storage tank 12 (S22). In addition, since step S22 is the procedure similar to step S14, detailed description is abbreviate | omitted. When the holding jig 40 is disposed in the fixing jig 20, the electrode portion 22 and the metal plate 4 face each other. Step S22 is an example of the “second immersion process”.

  Next, the connection portion 36 of the fixing jig 20 is connected to the anode of the power supply device 16, the connection portion 74 of the holding jig 40 is connected to the cathode of the power supply device 16, and between the two connection portions 36 and 74. A voltage is applied (S24). That is, in step S24, a voltage in the reverse direction to step S16 is applied. Then, a voltage is applied between the electrode portion 22 and the metal plate 4, and the metal deposit on the surface of the electrode portion 22 functioning as an anode is dissolved in the electrolyte solution 14. Thereby, the surface of the electrode unit 22 is cleaned.

  If a voltage is applied, the voltage value applied between the electrode part 22 and the metal plate 4 is measured (S26). Here, with reference to FIG. 7, the voltage value between the electrode part 22 and the metal plate 4 at the time of washing | cleaning of the electrode part 22 is demonstrated. FIG. 7A shows the relationship between the voltage value between the electrode portion 22 and the metal plate 4 and the time when the electrode portion 22 is cleaned. FIG. 7 (b) shows, as a comparative example, the relationship between the voltage value between the stainless steel electrode and the metal plate 4 and the time at the time of cleaning of the electrode portion formed of stainless steel (hereinafter also referred to as stainless steel electrode). There is. In the present embodiment, a constant current source is used for the power supply device 16.

  When a voltage is applied between the electrode portion 22 and the metal plate 4, the metal deposit on the surface of the electrode portion 22 dissolves, while the electrode portion 22 formed of titanium does not dissolve. Therefore, as shown in FIG. 7A, when a constant current flows between the electrodes, as the metal deposit attached to the surface of the electrode portion 22 dissolves in the electrolyte solution 14, the electrode portion 22 and the metal plate 4 The electrical resistance between them gradually rises. Therefore, the voltage applied between the electrode portion 22 and the metal plate 4 also increases. When almost all the metal deposit on the surface of the electrode portion 22 is dissolved, the electrical resistance between the electrode portion 22 and the metal plate 4 becomes constant, and the voltage value of the voltage applied between both becomes constant. Therefore, by measuring the voltage value between the electrode portion 22 and the metal plate 4, it is possible to detect the state of dissolution of the metal deposit on the surface of the electrode portion 22. On the other hand, when a voltage is applied between the stainless steel electrode and the metal plate 4, the metal deposit on the surface of the stainless steel electrode is dissolved, and the stainless steel electrode itself is also dissolved. For this reason, as shown in FIG. 7 (b), when a constant current flows between the electrodes, the stainless steel electrode itself continues to dissolve even after all the metal deposit is dissolved, so the electrical resistance becomes substantially constant, and the voltage value It becomes almost constant. Therefore, even if the voltage value between the stainless steel electrode and the metal plate 4 is measured, the state of dissolution of the metal deposit on the surface of the stainless steel electrode can not be detected.

  Next, it is determined whether the voltage value measured in step S26 is equal to or greater than a threshold (S28). As described above, when almost all the metal deposit on the surface of the electrode portion 22 is dissolved, the voltage value becomes substantially constant. For this reason, in the present embodiment, the threshold value is set based on the voltage value when almost all the metal deposit is dissolved. For example, in the example shown to Fig.7 (a), a threshold value can be set with 20V. Therefore, by determining whether the measured voltage value has reached the threshold value, it can be determined that the dissolution of the metal deposit attached to the surface of the electrode portion 22 has ended. If the voltage value has not reached the threshold (in the case of NO in step S28), it is determined that all the metal deposits attached to the electrode portion 22 have not dissolved, and the process returns to step S26 and the voltage is reached until the voltage reaches the threshold. Continue the cleaning process while continuing to measure the value. When the voltage value is equal to or higher than the threshold (in the case of YES in step S28), it is determined that the dissolution of the metal attached to the electrode unit 22 is completed, the application of the voltage is stopped, and the cleaning process is ended. By monitoring the voltage value in this manner, it is possible to prevent the cleaning process time from being unnecessarily long. Steps S24 to S28 are an example of the “second voltage application process”.

  In the decontamination method using the decontamination apparatus 10 of the present embodiment, the radioactive metal waste 2 is held without taking out the fixing jig 20 for fixing the electrode unit 22 functioning as a cathode at the time of decontamination from the storage tank 12 The holding jig 40 can be removed from the storage tank 12. Therefore, the metal plate 4 can be disposed in the storage tank 12 instead of the radioactive metal waste 2 while the electrode portion 22 is disposed in the storage tank 12. Therefore, there is no need to take out the electrode part 22 from the storage tank 12 when the electrode part 22 is cleaned, and the work load can be reduced.

  Although the voltage value is measured in step S26 in the present embodiment, the present invention is not limited to such a configuration. As long as the state of dissolution of the metal deposit on the surface of the electrode unit 22 can be detected, for example, the current value between the electrode unit 22 and the metal plate 4 may be measured using a constant voltage source for the power supply device. In this case, as the metal deposit dissolves, the electrical resistance between the electrode portion 22 and the metal plate 4 increases, so the current value of the current flowing between the both decreases. Then, when almost all the metal deposit on the surface of the electrode portion 22 is dissolved, the electric resistance between the electrode portion 22 and the metal plate 4 becomes constant, and the current value also becomes constant. Therefore, by measuring the value of the current flowing between the electrode portion 22 and the metal plate 4, the state of dissolution of the metal deposit on the surface of the electrode portion 22 can be detected.

  Moreover, although the cleaning process of the electrode part 22 is performed whenever the decontamination process of the radioactive metal waste 2 is complete | finished in the decontamination method of a present Example, it is not limited to such a structure. For example, the cleaning process of the electrode unit 22 may be performed after it is determined that a large amount of metal deposit adheres to the surface of the electrode unit 22 and the decontamination ability is reduced below a certain level. That is, after the decontamination treatment of the radioactive metal waste 2 is completed, the decontamination treatment of another radioactive metal waste 2 may be repeated to wash the electrode portion 22 when the decontamination ability is lowered. .

  Further, in the present embodiment, the inner surface of the cylindrical radioactive metal waste 2 is electropolished using the decontamination apparatus 10, but the present invention is not limited to such a configuration. For example, a flat radioactive metal waste may be placed on the holding jig 40, and the surface of the flat radioactive metal waste may be electropolished.

  The specific examples of the technology disclosed in the present specification have been described above in detail, but these are merely examples, and do not limit the scope of the claims. The art set forth in the claims includes various variations and modifications of the specific examples illustrated above. The technical elements described in the present specification or the drawings exhibit technical usefulness singly or in various combinations, and are not limited to the combinations described in the claims at the time of filing.

2: radioactive gold storage waste 4: metal plate 10: decontamination apparatus 12: storage tank 14: electrolyte solution 16: power supply device 20: fixing jig 22: electrode unit 24: lower plate 38: guide unit 40: holding jig 48a : Guide hole 50: grip portion 52: first members 60a, 60b: edge 62: second member 66: shock absorbing material 80: guide hole

Claims (5)

A decontamination apparatus for decontaminating radioactive metal waste by electropolishing, comprising
A storage tank in which the electrolytic solution is stored;
Power supply,
A first electrode which can be disposed in the storage tank and electrically connected to the power supply device;
A connecting member electrically connected to the power supply device and selectively connected to the radioactive metal waste and the second electrode;
The connection member is a first position where the radioactive metal waste or the second electrode is disposed in the reservoir while the first electrode is disposed in the reservoir, and the storage is performed. It can be switched to the second position where the radioactive metal waste or the second electrode is disposed outside the tank,
The connection member is at the first position in a state of being connected to the radioactive metal waste, and the power supply device is configured such that the first electrode becomes a cathode and the radioactive metal waste becomes an anode. Decontaminate the radioactive metal waste by electropolishing by applying a voltage to the
By setting the connection member to the second position in a state where the first electrode is disposed in the storage tank, a member connected to the connection member outside the storage tank is the radioactive metal waste and Switch between 2 electrodes,
In the state where the connection member is connected to the second electrode, the first position is set, and the power supply device is configured such that the second electrode becomes a cathode and the first electrode becomes an anode. The decontamination apparatus which wash | cleans the metal deposit | attachment adhering to a said 1st electrode by applying a voltage to this.   The decontamination apparatus according to claim 1, wherein the first electrode is formed of a metal belonging to a titanium group. The radioactive metal waste is cylindrical,
The connection member is provided with a gripping portion for gripping the radioactive metal waste so that the axial direction of the radioactive metal waste is vertical when the connection member is positioned at the first position. The decontamination apparatus according to claim 1 or 2. A decontamination method for decontaminating radioactive metal waste by electropolishing, comprising:
A first immersing step of immersing the radioactive metal waste electrically connected to a power supply device in an electrolyte;
A voltage in a forward direction between the radioactive metal waste immersed in the electrolytic solution by the first immersing step, and a first electrode disposed in the electrolytic solution and electrically connected to the power supply device A first voltage application step of applying
Taking out the radioactive metal waste from the electrolytic solution in a state where the first electrode is disposed in the electrolytic solution;
A second immersing step of immersing a second electrode electrically connected to the power supply device into the electrolytic solution after the removing step;
A second voltage application step of applying a voltage in a reverse direction to the first electrode and the second electrode immersed in the electrolytic solution in the second immersion step. The first electrode is formed of a metal belonging to a titanium group,
In the second voltage application step, at least one of a voltage applied between the first electrode and the second electrode, and a current flowing between the first electrode and the second electrode The decontamination method according to claim 4, wherein application of a reverse voltage between the first electrode and the second electrode is stopped based on the following.

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